Due to the two-dimensional nature of drawing atomic interactions, (short of using powerful computational tools such as SPARTAN), organic chemists have resorted to drawing out the different ways electrons can travel around.
For example, for benzene rings, the alternating structure of double bonds in the ring like structure are often drawn as a ring.
Where an abbreviated method cannot be used, usually a doubleheaded arrow is used to show the difference in resonance structures.
[diagrams soon to come]